CHAPTER VIII. 



SYSTEMATIC ACCOUNT OF THE FRESHWATER FISHES 



OF BRITISH GUIANA. 



Class SELACHII. 



Order BATOIDEI. 



Suborder MASTICURA. 



Whip-tailed Rays. 



Family I. DASYATID.E. 



Tail abruptly slender, its back usually with a serrated spine; pectoral fins 

 uninterrupted, confluent around the snout; teeth small; nasal valves forming a 

 flap, which is joined to the upper jaw by a narrow frenum; spiracles large. 



Subfamily Potamotrygonin^e. 

 Pelvis with a sword-shaped cartilage extending forward in the mid-ventral line. 



Key to the Guiana Genera of Potamotrygonin^e. 

 a. Tail with irregular thorns on its upper surface, and with a large spine. 



6. Mouth with papilla?; teeth in more than twenty-five rows Potamotrygon. 



66. Mouth without papilla 1 ; teeth in less than twenty-five rows Paratrygon. 



an. Tail with many short spines about its base Elipesurus. 1 



Potamotrygon Carman. 

 Tamiura Muller and Henle, Bericht. K. Preuss. Akad. Wiss., 1837, 117 {ornatum). 

 Potamotrygon Garman, Proc. Bost. Soc. Nat. Hist., 1877, 210. 

 Type, Pastinaca humboldtii Roulin. 



1. Potamotrygon hystrix (Muller and Troschel). 

 ? Pastinaca humboldtii Roulin, Ann. Sc. Nat,, XVI, 1829, 104, pi. 3 (Meta).- 



Dumeril, Hist. Nat, Poiss., I, 1865, 625 (copied). 

 Potamotrygon humboldtii Carman, Proc. Bost, Soc. Nat, Hist,, 1877, 210. 

 Trygon hystrix Muller and Henle. Syst. Beschr. Plagiostomen, 1841, 167. — Val- 



1 Elipesurus was taken by Schomburgk in the Rio Braneo, and may occur in the Essequibo basin also. 



116 



